Composite wires for coating substrates and methods of use

ABSTRACT

A composite wire utilized in connection with forming a resistant coating on a substrate includes a metallic outer sheath and an inner core, the inner core having a total fill weight above 15% total composite wire weight and including less than less 35% by weight of boron carbide in the inner core, and method of making the same.

TECHNICAL FIELD

The present invention relates generally to composite wires utilized in the coating various substrates, particularly metallic substrates. More specifically, the invention relates to composite wires or cored wires for forming wear-resistant and corrosion-resistant coatings on metallic substrates by thermal spraying processes, spray and fuse processes, or by welding techniques. The invention also relates to methods of employing the composite to apply wear-resistant and corrosion-resistant coatings to substrates.

BACKGROUND

Thermal spraying, i.e. the generic name for a class of processes that allow the depositing molten or semi-molten materials onto a substrate to form a wear or corrosion resistant coating, has been known in various forms for many years. Thermal spraying processes include plasma, flame, arc-plasma, arc and combustion spraying. Arc spraying is a form of thermal spraying which involves feeding two electrically conductive wires towards one another so that an arc is struck between the tips of the wires to melt the wire tips. The molten material is then atomized and sprayed onto a substrate by compressed gas.

This form of thermal spraying is widely used to provide corrosion-resistant coatings on various metallic articles.

Generally, the binder metal (i.e., the metal of the outer sheath) in a wear-resistant coating is critical to the performance of the coating in corrosive conditions such as those encountered in, e.g., boilers. Composite wires for forming wear resistant coatings are known wherein the wire is formed of an alloy sheath having iron, nickel, or cobalt as a major component. The core of the composite wire is formed of powder that includes boron or boron carbide. Due to its extreme hardness, boron carbide is employed in coatings where wear or abrasion is of primary concern. However, as with other conventional composite wires in high-temperature corrosive environments, the wear resistant coatings may experience accelerated wear nonetheless.

Despite, therefore, the composite wires known in the art, there is a need for composite wires that evidence even a greater degree of corrosion and wear resistance.

BRIEF DESCRIPTION OF THE INVENTION

In an embodiment, a method of forming a resistant coating on a substrate includes providing a wire having a metallic outer sheath and an inner core; effecting a total fill weight of the inner core to be above 15% total composite wire weight; including less than 35% by weight of boron carbide in the inner core; melting the wire to form a melt; and atomizing and spraying the melt onto a substrate.

In another embodiment, a method of forming a resistant coating on a substrate includes providing a wire having a metallic outer sheath and an inner core; effecting a total fill weight of the inner core to be between 15% and 50%; including less than 35% by weight of boron carbide in the inner core; melting the wire to form a melt; and atomizing and spraying the melt onto a substrate.

In another embodiment, a composite wire utilized in connection with forming a resistant coating on a substrate is provided. The wire includes a metallic outer sheath and an inner core, the inner core having a total fill weight above 15% total composite wire weight and the inner core includes less than 35% by weight of boron carbide.

In yet another embodiment, a composite wire is provided. The composite wire includes a metallic outer sheath and an inner core, the inner core having a total fill weight of up to about 70%, with the outer sheath including one of an iron or an iron-alloy. The inner core includes chrome carbide and less than 35% by weight of boron carbide, the chrome carbide and the boron carbide being present in the inner core in approximately the same weights.

DRAWINGS

The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:

FIG. 1 is a cross-sectional view of a composite wire, according to an embodiment of the invention.

FIG. 2 is a chart showing the Gibbs energy minimization plots for the coating system of the present invention.

DETAILED DESCRIPTION

In the following detailed description of the preferred embodiments, it is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention.

The coatings according to the present invention are specifically designed for articles subjected to wear and/or corrosion. Such articles include, but are not limited to, boiler tubes, hydraulic piston rods, pump casings, rollers in the paper and steel industry, wear plates, journals and shafts, and turbine blades and casings. Accordingly, as used herein, the term “resistant coating” means a coating that is resistant to corrosion, erosion, abrasion, and/or wear.

The coatings of the present invention are formed from composite wires, which are fed through a conventional arc spraying apparatus, such as the apparatus disclosed in PCT Patent No. WO 01/08810 (Seitz), the disclosure of which is incorporated herein by reference.

As shown in FIG. 1, a composite wire(s) 100 of the present invention includes an outer sheath 102 formed from a metal or alloy. In one embodiment of the invention, which is particularly suited for the high temperature erosion-corrosion environment found in, e.g., boiler applications, the composite wire 100 includes an outer tubular sheath 102 formed from a chromium bearing, nickel base alloy such as an alloy 625, and an inner core 104, which includes boron carbide and chrome carbide.

In an embodiment, the inner core formulation includes chrome carbide in an amount between about 25% and about 400% by weight of the amount of boron carbide. In other words, the ratio of chrome carbide to boron carbide ranges between about 1:4 to about 4:1. More specifically, the inner core includes chrome carbide in an amount between about 67% and about 230% by weight of the amount of boron carbide. In other words, the ratio of chrome carbide to boron carbide ranges between about 1:1.5 to about 2.3:1. In one embodiment, the inner core includes about 100% by weight of chrome carbide relative to the amount of boron carbide, in other words the amounts of chrome carbide and boron carbide are substantially the same.

As is generally known, the chrome carbide in the inner core increases the wear resistance of the deposited coating or weld overlay. The chrome carbide is retained during the thermal spraying or welding, and is present in molten form within the coating structure during application. However, this benefit accrues on a sliding scale—the more chrome carbide used the better the result, but at the expense of displacing boron carbide and its beneficial effects. Conversely, most of the boron carbide does not appear to survive as a carbide during application of the coating. The boron carbide breaks up in the arc as uncontaminated boron and carbon, which both have substantial hardening effects. The hardening effect increases the hardness of the metal of the outer sheath through alloying and/or diffusion processes. Some of the larger particles of boron carbide may survive the arc. Those particles add to the wear resistance, much like the chrome carbide, but the resistance achieved with large particles of boron carbide is not as effective as that achieved with chrome carbide. Furthermore, the boron carbide inhibits the formation of oxides in the molten outer sheath during spraying. To achieve this result, a sufficient amount of boron carbide should be present in the inner core.

In many composite wires, it has been believed that a total fill weight of the core material should not exceed approximately 22% total composite wire weight, in order to provide suitable functional and operational efficiencies, such as appropriate ductility of the cord itself. Moreover, it was also generally believed in the art that at least about 35% by weight of the inner core should consist of boron carbide to achieve suitable low oxide formation in the resultant coating, amongst other benefits.

In contrast, the present invention has discovered that, in one embodiment, if the total fill weight of the core material is increased above 15% total composite wire weight, it would then be possible to reduce the amount of boron carbide by weight in the core material. Indeed, by increasing the total fill weight of the core material above 15% total composite wire weight, it is possible to utilize additional metals, cermets, and ceramic powders in the core material, so as to counteract any potential undesirable effects of reducing the boron carbide content below 35% by weight of the core material.

In another embodiment of the present invention, it is proposed to increase the total fill weight of a composite cord to 50%, while reducing the overall use of boron carbide to be below 35% by weight of the core material.

In yet another embodiment of the present invention, it is proposed to increase the total fill weight up to 70%, while utilizing boron carbide in the range of 1-50% by weight, chromium carbide in the range of 1-50% by weight, with the use of additional metals, cermets, and/or ceramic additives in the range of 2-99% by weight of the core material.

The diameter of the composite wire 100 of the present invention is envisioned to be in the range of 0.0625-0.150 inches. In other embodiments, the diameter is envisioned to be in the range of 0.0315-0.252 inches. Moreover, it will be readily appreciated that the composite wire of the present invention is especially useful in applications where composite wires having larger diameters are desired.

Indeed, the present invention has determined that when using composite wires having a total fill weight greater than 15% total composite wire weight, it is also possible to utilize metals other than chromium in the core material, thereby realizing economic savings while maintaining performance.

Turning now to FIG. 2, a chart 200 depicting Gibbs energy minimization plots is shown. As suggested in chart 200, it is envisioned that one embodiment of the present invention involves a composite wire having a total fill weight of over 15% total composite wire weight, and a core composition that includes a Fe—Cr matrix with predominately iron borides (FeB) and chromium borides (CrB) with some amounts of hafnium carbide (HfC)/boride (HfB2) and tantalum carbide (TaC)/boride (TaB2) around a temperature regime of 1500 C-2500 C.

As discussed, while the inner core formulation of the present invention centers around chrome carbide and boron carbide, the inner core may also contain additional materials. The additional materials may include: carbides, such as tungsten carbide, titanium carbide, vanadium carbide, and the like; oxides, such as aluminum oxide, chrome oxide, zirconium oxide, and the like; and borides, such as chrome boride, nickel boride, iron boride, and the like. The inner core may also include additional metal powders such as aluminum, nickel, chrome, or alloy powder, or composite powders such as tungsten carbide nickel and chrome carbide nickel chrome powders.

As is also known, the grain size of the chromium carbide and boron carbide will have an effect on the physical properties of the applied coating. Generally, the finer the grains of the carbides, the more homogenous the coating will be and generally the better the wear and corrosion properties. However, the cost and manufacturing constraints will limit the lower end of the grain size range. U.S. Pat. No. 4,741,974 (Longo, et al.), the disclosure of which is hereby incorporated by reference, discloses the effect of grain size with respect to boron carbide.

While alloy 625 is an alloy for the outer sheath of the composite wire suitable for use in certain high temperature erosion-corrosion applications, alternative metals and alloys can also be employed. For example, alternative chrome bearing nickel base alloys include alloy C-276, alloy 686, or alloy 690. INCONEL® C-276, alloy 686, and alloy 690, which are all produced by the Special Metals Corporation contains: 0.02% C, 1.0% Mn, 4.0%-7.0% Fe, 0.04% P, 0.03% S, 0.08% Si, 0.5% Cu, bal. Ni, 2.5% Co, 14.5%-16.5% Cr, 15.0%-17.0% Mo, 3.0%-4.5% W (INCONEL® C-276); 0.01% C, 1.0% Mn, 5.0% Fe, 0.02% P, 0.02% S, 0.08% Si, 0.5% Cu, bal. Ni, 0.5% Al, 0.25% Ti, 19.0%23.0% Cr, 15.0%-17.0% Mo, 3.0%-4.40% W. (INCONEL® alloy 686); and 0.02% C, 1.0% Mn, 7.0%-11.0% Fe, 0.015% S, 0.5% Si, 0.5% Cu, bal. Ni, 27%-31% Cr (INCONEL® alloy 690). Nickel copper alloys, such as alloy 400, alloy R-405, and the like, and nickel molybdenum alloys such as, alloy B, alloy B-2, and the like, may also be employed depending on the required physical properties of the resulting coating and the environment to which the coating will be exposed.

As stated above, the metal binder material is not limited to nickel base alloys, rather the outer sheath may be constructed of any metal or alloy. Additional suitable binder material includes, but is not limited to, iron, carbon and low alloy steels, stainless steels, nickel, copper, copper alloys (e.g., brasses, bronzes, and aluminum bronzes) aluminum, aluminum alloys (e.g., aluminum-copper, aluminum-manganese, aluminum-manganese-magnesium, aluminum-silicon, aluminum-manganese-magnesium-chrome, aluminum-magnesium-silicon, and aluminum-zinc-manganese-magnesium-copper), titanium, titanium alloys (e.g., titanium alloyed with palladium, molybdenum, nickel, aluminum, vanadium, niobium, tantalum, tin, zirconium, chromium and iron), cobalt, cobalt alloys (e.g., cobalt alloyed with chromium, nickel, molybdenum, and tungsten), zirconium, zirconium alloys, tantalum and tantalum alloys. The combination of any of these binders with the inner core powder of the present invention results in coatings having superior physical properties over conventional coatings.

Indeed, in another embodiment of the present invention, it is proposed to increase the total fill weight above 15% total composite wire weight, while utilizing boron carbide in the range of 1-50% by weight, chromium carbide in the range of 1-50% by weight, with the use of additional metals, cements and/or ceramic additives in the range of 2-99% by weight of the core material, in combination with forming the sheath of the composite wire from an iron-based alloy.

In manufacture, the composite wires of the present invention may be formed in any conventional manner, such as by placing the mix of carbides, which need not be an agglomerated mix, onto an alloy 625 strip, or a strip of some other outer sheath alloy, which is drawn continuously through a plurality of wire drawing dies to form an outer wire sheath around an inner carbide core. The final outer diameter of the composite wire will depend upon the application for which it is used. As discussed previously, the composite wires of the present invention can enjoy a final diameter range between about 0.8 mm to about 6.4 mm.

Although the present invention has been described in terms of specific embodiments, it is anticipated that alterations and modifications thereof will no doubt become apparent to those skilled in the art. It is therefore intended that the following claims be interpreted as covering all alterations and modifications that fall within the true spirit and scope of the invention.

For example, embodiments of the present invention provide for a method of forming a resistant coating on a substrate. The method includes the steps of: providing a wire having a metallic outer sheath and an inner core; effecting a total fill weight of the inner core to be above 15% total composite wire weight; including less than 35% by weight of boron carbide in the inner core; melting the wire to form a melt; and atomizing and spraying the melt onto a substrate. In certain embodiments, the melt includes the metal of the sheath and material in the inner core. In certain embodiments, the method further includes the step of forming the outer sheath of an essentially pure metal. In certain embodiments, the method further includes the step of forming the outer sheath from an alloy including a base metal. In certain embodiments, the method further includes the step of selecting the base metal of the alloy from the group consisting of iron, nickel, aluminum, molybdenum, tantalum, copper, cobalt, and titanium. In certain embodiments, the method further includes the step of forming the alloy to be an iron base alloy. In certain embodiments, the method further includes the step of forming the iron base alloy to further include chromium. In certain embodiments, the method further includes the step of forming the iron base alloy to have at least about 40% by weight of iron. In certain embodiments, the method further includes the steps of forming the inner core to include chrome carbide. In certain embodiments, the method further includes the step of forming the inner core to exhibit a ratio of the chrome carbide to the boron carbide to be between about 1:4 to 4:1. In certain embodiments, the method further includes the step of forming the inner core further to include another carbide in addition to boron carbide and chrome carbide. In certain embodiments, the method further includes the steps of forming the inner core to include at least one carbide selected from the group consisting of tungsten carbide, vanadium carbide and titanium carbide.

Other embodiments of the present invention provide for a method of forming a resistant coating on a substrate. The method includes the steps of: providing a wire having a metallic outer sheath and an inner core; effecting a total fill weight of the inner core to be between 15% and 50% total composite wire weight; including less than 35% by weight of boron carbide in the inner core; melting the wire to form a melt; and atomizing and spraying the melt onto a substrate. In certain embodiments, the inner core includes a metal powder. In certain embodiments, the inner core includes a composite powder.

Further embodiments of the present invention provide for a composite wire utilized in connection with forming a resistant coating on a substrate. The composite wire includes a metallic outer sheath and an inner core, the inner core having a total fill weight above 15% total composite wire weight. The inner core includes less than 35% by weight of boron carbide. In certain embodiments, the inner core has a total fill weight to be between 15% and 50% total composite wire weight. In certain embodiments, the inner core includes a metal powder. In certain embodiments, the inner core includes a composite powder.

Yet still further embodiments of the present invention provide for a composite wire utilized in connection with forming a resistant coating on a substrate. The composite wire includes a metallic outer sheath and an inner core, the inner core having a total fill weight up to about 70%, and the outer sheath including one of an iron and an iron alloy. The inner core includes less than 35% by weight of boron carbide, the inner core further includes chrome carbide; and the chrome carbide and the boron carbide are present in the inner core in approximately equal weights.

In yet another embodiment, a composite wire is provided. The composite wire includes a metallic outer sheath and an inner core, the inner core having a total fill weight of between 15%-50% total composite wire weight, and includes less than 35% by weight of boron carbide.

In yet another embodiment, a method is provided. A method of forming a resistant coating on a substrate, the method including the steps of: providing a wire having a metallic outer sheath and an inner core, forming the inner core to include iron or an iron alloy, effecting a total fill weight of the inner core to be up to about 70%, including less than 35% by weight of boron carbide in the inner core, further including chrome carbide in the inner core, melting the wire to form a melt, and atomizing and spraying the melt onto a substrate.

In yet another embodiment, a method of forming a resistant coating on a substrate is provided. The method includes the steps of: providing a wire having a metallic outer sheath and an inner core, forming the inner core to include iron or an iron alloy, effecting a total fill weight of the inner core to be up to about 70%, including less than 35% by weight of boron carbide in the inner core, further including chrome carbide in the inner core wherein the chrome carbide and the boron carbide are present in the inner core in approximately equal weights, melting the wire to form a melt, and atomizing and spraying the melt onto a substrate.

This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Additionally, while the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, terms such as “first,” “second,” “third,” “upper,” “lower,” “bottom,” “top,” etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format are not intended to be interpreted based on 35 U.S.C. §112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.

This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional such elements not having that property.

Since certain changes may be made in the above-described invention, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention. 

What is claimed is:
 1. A method of forming a resistant coating on a substrate, the method comprising the steps of: providing a wire having a metallic outer sheath and an inner core; effecting a total fill weight of the inner core to be above 15% total composite wire weight; including less than 35% by weight of boron carbide in the inner core; melting the wire to form a melt; and atomizing and spraying the melt onto a substrate.
 2. The method of claim 1, wherein: the melt comprises the metal of the sheath and material in the inner core.
 3. The method of claim 1, the method further comprising the step of: forming the outer sheath of an essentially pure metal.
 4. The method of claim 1, the method further comprising the step of: forming the outer sheath from an alloy comprising a base metal.
 5. The method of claim 4, the method further comprising the step of: selecting the base metal of the alloy from the group consisting of iron, nickel, aluminum, molybdenum, tantalum, copper, cobalt, and titanium.
 6. The method of claim 4, the method further comprising the step of: forming the alloy to be an iron base alloy.
 7. The method of claim 6, the method further comprising the step of: forming the iron base alloy to further comprise chromium.
 8. The method of claim 7, the method further comprising the step of: forming the iron base alloy to have at least about 40% by weight of iron.
 9. The method of claim 1, the method further comprising the step of: forming the inner core to include chrome carbide.
 10. The method of claim 9, the method further comprising the step of: forming the inner core to exhibit a ratio of the chrome carbide to the boron carbide to be between about 1:4 to 4:1.
 11. The method of claim 9, the method further comprising the step of: forming the inner core further to comprises another carbide in addition to boron carbide and chrome carbide.
 12. The method of claim 1, the method further comprising the step of: forming the inner core to include at least one carbide selected from the group consisting of tungsten carbide, vanadium carbide and titanium carbide.
 13. A method of forming a resistant coating on a substrate, the method comprising the steps of: providing a wire having a metallic outer sheath and an inner core; effecting a total fill weight of the inner core to be between 15% and 50% total composite wire weight; including less than 35% by weight of boron carbide in the inner core; melting the wire to form a melt; and atomizing and spraying the melt onto a substrate.
 14. The method of claim 13, wherein the inner core includes a metal powder.
 15. The method of claim 13, wherein the inner core includes a composite powder.
 16. A composite wire utilized in connection with forming a resistant coating on a substrate comprising: a metallic outer sheath and an inner core, the inner core having a total fill weight above 15% total composite wire weight; and wherein the inner core includes less than 35% by weight of boron carbide.
 17. The composite wire of claim 16 wherein the inner core has a total fill weight to be between 15% and 50% total composite wire weight.
 18. The composite wire of claim 16, wherein the inner core includes a metal powder.
 19. The composite wire of claim 16, wherein the inner core includes a composite powder.
 20. A composite wire utilized in connection with forming a resistant coating on a substrate comprising: a metallic outer sheath and an inner core, the inner core having a total fill weight up to about 70%, and the outer sheath including one of an iron and an iron alloy; wherein the inner core includes less than 35% by weight of boron carbide; wherein the inner core further includes chrome carbide; and wherein the chrome carbide and the boron carbide are present in the inner core in approximately equal weights. 